Cutting implement with cartridge

ABSTRACT

A utility knife has a receiving cavity which opens through the body. A cartridge comprising a magazine of blades is removably insertable into the receiving cavity. A carrier within the body is manually operable for receiving a blade from the cartridge and positioning the blade for extension through the opening to present a cutting edge. The cartridge may be released from the utility knife body by depressing a button and withdrawing the cartridge. The cartridge is releasably held in place within the knife body and releasable when the blade carrier is in its retracted position and the release button is depressed. When the thumb button moves the blade carrier into its extended position to expose the knife blade, the cartridge is rendered unreleaseable even if the release button is depressed. The release button, which will enable removal of the magazine when depressed and blade carrier is in its retracted position, also serves to release of the blade from the blade carrier to permit removal of a used blade from the knife body when the blade carrier is in its extended position.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority of U.S. Patent Application No.60/789,530 filed on Apr. 4, 2006.

TECHNICAL BACKGROUND

This invention relates generally to blade loading systems for trimmingand cutting devices. More particularly, this invention relates to kniveswhich are loadable with a plurality of blades for sequential slidingmovement to a forward position to present a cutting edge for usage.

SUMMARY

Briefly stated, a knife comprises a body having a handle portion with afrontal opening for a blade and a receiving cavity opening through thebody. A cartridge comprising a magazine of blades is insertable into thereceiving cavity. A carrier is manually operable for receiving the bladefrom the cartridge and positioning the blade for extension through theopening to present a cutting edge. A button projects through the bodyand is manually depressable to release the blade from the carrier topermit withdrawal forwardly from the opening. The button may also bedepressable to allow the cartridge to be withdrawn from the body.

The cartridge forms a receptacle for receiving a plurality of blades andthe receptacle defines a detent which interacts to secure the cartridgeto the body. A pivoted lever arm mounted interiorally to the body at oneend connects to the button and a second end engages the cartridge toretain the cartridge in the body. The cartridge has an exterior surfacewhich mates with a body upon reception in the receiving cavity. A windowopens through the exterior surface to allow visual inspection of bladesin the cartridge. The cartridge has a frame and a cover which snaps intothe frame to capture the blades. A biasing member may be mounted intothe interior of the cover. The frame and cover prevent direct contactwith cutting portions of the blades.

The blades are preferably substantially congruent and further includethree notches in an upper location thereof. The blades may take variousforms such as a trapezoidal shape, a hook-type shape or a hawk-typeshape. To enhance versatility, a second cartridge has a magazine ofblades with a different configuration from those of the first cartridge.

The cartridge may be a molded member. An overmold substantially definesthe exterior of the knife body. In one embodiment, the cover furthercomprises a plurality of projections which form a one time lock with theframe.

According to another aspect a utility knife is provided which comprisesa body having a handle portion and a frontal opening for a blade and areceiving cavity opening into body. A cartridge containing a pluralityof blades is insertable into said receiving cavity. The cartridge hasfront and rearward tabs. A blade carrier is manually operable forreceiving a blade from said cartridge and moveable into an extendedposition to position said blade through said opening into a cuttingposition. The front and rearward cartridge catches are adapted toreleaseably engage said tabs to secure said cartridge in said body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a utility knife;

FIG. 2 is a side elevational view of a second embodiment of a utilityknife;

FIG. 3 is an exploded perspective view, partly in schematic, of theutility knife of FIG. 1;

FIG. 4 is an interior bottom plan view, partly in schematic,illustrating a sub-assembly of the utility knife of FIG. 3;

FIGS. 5A, 5B, and 5C are perspective views of the blade cartridge ofFIG. 4 from the various sides thereof and illustrating various cartridgeembodiments;

FIG. 6 is an exploded perspective view of a blade cartridge of FIG. 5;

FIG. 7 is a second perspective view of the cartridge of FIG. 5 from agenerally opposite location thereof;

FIG. 8 is a fragmentary enlarged perspective view illustrating a forwardtop frontal portion of the utility knife of FIG. 1;

FIG. 9A-9C are side views of alternative blade embodiments for thevarious utility knives;

FIG. 10 is an isometric side view of a second aspect of a utility knifeshowing the knife body and removable cartridge;

FIG. 11 is an exploded view of the blades and cartridge of the aspectshown in FIG. 10;

FIG. 12 is an isometric view of the assembled blades and cartridge ofFIG. 11;

FIG. 13 is a partial sectional view of the knife body and insertedcartridge with the opening in the knife body for the blade to be exposedbeing to the left as view in the Figure;

FIG. 14 is a partial sectional view of the knife body and cartridge withthe opening in the knife body for the blade to be exposed being to theright as view in the Figure;

FIG. 15 is a view similar to FIG. 14 , but showing the thumb button andblade carrier being moved into the extended position;

FIG. 16 is a partial sectional view similar to FIG. 14, but showing thethumb button and blade carrier in the extended position with the bladein a positioned to cut;

FIGS. 17 a-d are side views of the various stages of a hobby knifehaving a removeable blade cartridge; and

FIGS. 18 a-d are isometric views of the various stages of a trimmerhaving a removeable blade cartridge.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the drawings wherein like numerals represent likeparts throughout the several Figures, a utility knife is designated withthe numeral 10 in FIG. 1 and 10A in FIG. 2. The utility knife 10receives a cartridge 20 comprising a sealed magazine of blades 30 whichare sequentially projectable to a forward position to present a cuttingedge 32 extending forwardly from the knife body 12.

The knife body 12 includes a receiving cavity 13 which is dimensionedand configured to complement the cartridge 20 as best illustrated inFIG. 3. The receiving cavity 13 in the illustrated embodiment has anunderside access opening so that the cartridge may be inserted throughthe access opening (shown by the arrow) into the knife body and snappedinto a secure retention therewith.

At the interior of the knife body 12, a blade carrier (not illustrated)is configured for sequentially receiving a blade and slidinglongitudinally in the body to project the blade through a frontalopening 14 of the utility knife to present a cutting edge 32. Thecarrier includes locating tabs (not illustrated) which mate with notches34 of the blade to allow the innermost blade to be projected by thecarrier. The upper body of the utility knife includes a longitudinalslot 16 (FIG. 8) which receives a resilient finger-like projectionconnecting the carrier and includes a button 18 to allow the carrier tobe moved by the user's thumb to the forward cutting position (shown inFIGS. 1, 2, 3 and 8) and to retract the blade into the housing formed bythe body.

The cartridge 20 may assume various forms such as illustrated in FIGS. 3and 5. The cartridge 20 includes a receptacle (trapezoidal asillustrated) frame 22 for receiving and protecting the blades 30 whichpreferably have three notches 34 at the upper portions thereof. Thecutting edges 32 of the blades engage a platform 24, the other side ofwhich forms a portion of the underside surface 36 of the knife body uponthe mounting of the cartridge into the blade or cartridge-receivingcavity 13. A cover plate 40 (FIGS. 6 and 7) includes four one-way treeextensions 42 which snap into openings 38 of the frame. The inner sideof the cover plate includes an integrated spring 44 which bears againstthe outermost blade and urges the blades toward the stop plate 46. Oncethe cover 40 is snapped into place, the blades are captured within thecartridge and the edges are sealed therewith so that access to theexposed cutting edges 32 is prevented prior to loading the cartridge inthe cavity.

In one embodiment, a release catch in the form of a detent 48 ispositioned at the side of the cartridge. With reference to FIG. 4, apivoted lever arm 50 is actuatable by a front button 52 and is pivotableso that the distal end of the lever arm has a latch 54 which engages inthe detent 48 to removably secure the cartridge. The cartridge retainingstructure may have other forms and alternative positions, such asretainers or catches 48A and 48B, (illustrated in FIG. 5).

Upon insertion of the cartridge 20 into the knife body 12, the undersidesurface 36 of the cartridge is integrated with the contoured surface ofthe body and the handle and includes a molded contoured grip portion 37to facilitate gripping and usage of the knife. In addition, a window 39is formed at the underside to allow viewing of the number of bladesremaining in the cartridge.

The utility knife 10, 10A functions in a highly efficient and safemanner. The cartridge 20 with the blade magazine is inserted into thereceiving cavity 13 of the knife body. The finger button 18 may beemployed so that the carrier receives the innermost blade and the fingerbutton is moved to force the blade through the frontal opening 14 to thecutting position. When it is desired to replace the blade, the frontalbutton 52 is depressed which forces the notches 34 to disengage from thecarrier retention tabs and allows the blade to be forwardly removed fromthe utility knife body. The finger button 18 may then be retracted topick up a new blade from the blade magazine which is forced against thecarrier by the spring 44 of the magazine. The newly received blade isthen projected to the forward position.

It will be appreciated that the button 52 in some embodiments functionsto both allow for ejection of the used blade and to release thecartridge for removal from the knife blade body. When it is desired toreplace the cartridge 20 entirely, there will be no blade in thecartridge and in the blade channel and accordingly pressing the button52 will allow release of the lever 50 to pivot and force the latch 54 todisengage from the detent 48 and the cartridge 20 to be manually removedfrom the blade body as schematically illustrated in FIG. 4. An arcuatedepression 58 in the body provides finger access for removing the spentcartridge.

The knife body preferably has a smooth contoured, aesthetically pleasingappearance with an overmold or outer layer which is configured tofacilitate gripping and usage of the utility knife. The outer layer isformed of a resilient and/or flexible polymer material, such as TPE. Thematerial may be overmolded over a rigid body portion which may be metalor an appropriate polymer such as ABS. The outer layer may be formed byan injection molding process or any other similar process used in theart. In addition, a finger channel 60 is formed at the upper portionaround the longitudinal extant of the slot 16. The finger channel 60 isalso provided with an overmold outer surface to facilitate usage of theutility knife.

Ribs 62 and grooves 64 molded to form exterior surface contours areconformably engaged by the hand during usage. The ribs and groovesprovide increased resiliency in areas of contact creating a cushioningeffect that relieves pressure on the hand and fingers during usage,thereby reducing fatigue and increasing comfort. The increasedresiliency helps maintain the grip and facilitates cutting precision.

In the illustrated embodiment the cartridge 20 is employed with aplurality of trapezoidal type cutting blades 30. However, with referenceto FIGS. 9A-9C it should be appreciated that hawk-type blades 30A,hook-type blades 30B and other type cutting blades 30C may also beloaded into a given cartridge.

The cartridge provides a very efficient and quick means for replacing anew blade magazine upon usage of the spent blades. In addition, becauseof the sealed package feature, the cartridge and the blades can behandled and loaded into the utility knife without the user's exposure tothe cutting edges of the blades.

It should be appreciated that in some embodiments the cartridge could beloaded from the side and snapped into position.

In accordance with another aspect shown in FIGS. 10-15, a utility knifebody 100 has an opening 102 in its bottom edge for reception of acartridge 104 having a plurality of blades 106 therein. The cartridge104 includes a front tab 108 on its front end and a rear tab 110 on itsrearward end that are adapted to be releasably engaged respectively by afront cartridge catch 112 and a rear cartridge catch 114 in the knifebody 100 as shown in FIG. 13. The cartridge 104 is adapted to beinserted in the bottom edge of the knife body 100 and locked in aposition by the front and rear cartridge catches 112 and 114 whereby ablade 106 in the cartridge 104 can be engaged by a blade carrier 116 andmoved forward by movement of the a thumb button 119 to extend from theforward opening 118 in the knife body 100 to present a cutting edge.

As shown in FIG. 12, the blades 106 include two spaced notches 120extending downwardly from their top edges. The cartridge 104 isgenerally trapezoidal and includes a frame 121 in which the blades arepositioned including a stop plate 122 against which the outer most blade106 rests. A back cover 123 is attached to the frame 121 by fingers 125that snap over side tabs 127 on the frame 121 or other suitableconnections. The frame 121 includes a base 129, the bottom surface ofwhich forms a portion of the undersurface of the knife body 100 when thecartridge 104 is inserted into the knife body 100. A spring 131 isattached to the inside of the back cover 123 to urge the blades 106toward the stop plate 122 in a position for the outermost blade 106 tobe engaged by the blade carrier 116. For the purposes of this aspect,the outermost blade is the blade positioned against the stop plate 122of the cartridge 104. The cartridge 104 includes a breakaway tab 124that extends over one of the notches 120 in the blades 106 with aportion 126 projecting downwardly into the notch 120 as shown in FIG.12. A tab 128 extends from the inner wall of the cartridge 104 into theother of the notches 120, terminating short of the inner wall of theoutermost blade 106. The breakaway tab 124 serves to contain the blades106 within the cartridge 104 during handling. When it is desired to usethe cartridge 104, the tab 124 is broken away just before the cartridge104 is inserted into the knife body 100.

As shown in FIGS. 13 and 14, the front cartridge catch 112 comprises apivotable member 132 having an upstanding arm 134 and a downwardlyextending arm 136 terminating in a hook 138 adapted to engage the tab108 on the front end of the cartridge 104 as shown. A spring 140 biasesthe pivotable member 132 and hook 138 into the latching position inengagement with the tab 108. The rear cartridge catch 114 includes alocking slide 142 that is urged forwardly by a spring clip 144 intoengagement with the rear tab 110 on the rearward end of the cartridge104.

A release button 146 is mounted in the side of the knife body 100. Therelease button 146 is adapted to provide for release of the cartridge104 when the blade carrier 116 is in its rearward position. In thisconnection, the release button 146 has a portion extending into theknife body 100 that has an inclined surface 148 thereon that is designedto mate with and engage an inclined surface 150 on the upstanding arm134 of the pivotable member 132 of the front cartridge catch 112 asshown in FIG. 13. With this arrangement, pushing inwardly on the releasebutton 146 to depress it moves the release button 146 in an axialdirection perpendicular to the longitudinal axis of the of knife body100 and parallel to the axis of rotation of the pivotable member 132 ofthe front cartridge catch 112. The interaction of the inclined surface148 on the release button 146 and the inclined surface 150 on theupstanding arm 134 of the pivotable member 132 causes the pivotablemember 132 to pivot about its pivot point 152 resulting in thedownwardly extending arm 136 pivoting away form the front end of thecartridge 104. This causes the hook 138 at the end of the downwardlyextending arm 136 to disengage from the front tab 108 on the cartridge104.

With the release button 146 depressed and the hook 138 disengaged fromthe front tab 108 on the cartridge 104, the cartridge 104 may be graspedby the fingers and pulled outwardly. For this purpose, the knife body100 may be provided with arcuate depressions 153 to provide fingeraccess for grasping the cartridge 104. As it is being pulled outwardly,after the front end is free, the cartridge 104 may pulled slightlyforward to release the rear tab 110 from the from the rear cartridgecatch 114 and then completely removed.

When the cartridge 104 is inserted into the knife body 100, it ispositioned so that the outermost blade 106 can be engaged by the bladecarrier 116. The blade carrier 116 is moveable within the knife body 100between a retracted position where it can engage a blade 106 in thecartridge 104 and a forward position wherein an engaged blade 106projects from the forward end of the knife body 100 and presents acutting surface. The blade carrier 116 is moveable between the twopositions by the thumb button 118 positioned on the top side of theknife body 100 and connected to the blade carrier 116 by a connectingmember 154 which extends through an elongated slot 156 in the top of theknife body 100. The blade carrier 116 includes a bracket member 158 towhich is attached a spring clip 160.

As shown particularly in FIG. 16, the spring clip 160 includes bladeengaging elements in the form of a front blade engaging tab 162 that isgenerally perpendicular to the length of the blade, and a rearward bladeengaging tab 164 which includes a horizontal portion 166 and anupstanding portion 168 which is angled inwardly toward the front of theknife body 100 as shown. The rearward blade engaging tab 164 projectsinto the rearward notch 120 in the blade 106 and engages the forwardedge of the notch 120 to move the blade 106 forwardly when the bladecarrier 116 is moved into the forward position. The angled upstandingsurface 168 serves to move the tabs 162 and 164 out of the way as theblade carrier 116 is being retracted after a blade has been released sothat the spring can pass over a blade 106 in the cartridge 104 as thecarrier 116 is being retracted. The front tab 158 projects into theforward notch 120 in the blade 106 and serves to engage the blade 106and pull the blade backward when the blade carrier 116 is beingretracted.

As shown in FIG. 16, when the blade carrier 116 is in its forwardposition and the blade 126 extends from the front of the knife body 110,the upstanding portion 168 of the rear blade engaging tab 164 is in aposition to be engaged by an inner extension 170 of the side releasebutton 146 as shown in FIG. 15. With this arrangement, depressing therelease button 146 will cause the tabs 162 and 164 to be disengaged fromthe notches 120 in the blade 106 so that the blade 106 may be removedfrom the knife body 100 by grasping the blade 106 and pulling it awayfrom the knife body 100.

The front and rear cartridge catches 112 and 114 are adapted to berendered unreleaseable when the blade carrier 116 is in the forwardposition and a blade is positioned for cutting. In this connection, asshown particularly in FIG. 13, the rear cartridge catch 114 includes apivotably mounted locking block 172 having an arm 174. The locking block172 is spring biased into a position behind the locking slide 142wherein it will prevent moment of the locking slide 142 away from thetab 110 on the cartridge 106. The arm 174 on the locking block 172 ispositioned to be engaged by the bracket 158 of the blade carrier 116when the blade carrier 116 is in its retracted position to pivot thelocking block 172 out of blocking engagement with the locking slide 142.

As shown in FIGS. 14 and 15, the front cartridge catch 112 includes asecurity lock 176 which is pivotally mounted for rotation about an axisperpendicular to the axis of rotation of the pivotable member 132. Thesecurity lock 176 is positioned below the axis of the pivotable member132 and includes a locking portion 178 which, when rotated into positionin front of the downwardly extending arm 136 on the pivotable member132, prevents the downwardly extending arm 136 and hook 138 from beingable to pivot out of engagement with the front tab 108 on the cartridge104. When the locking potion 178 is pivoted away from in front of thedownwardly extending arm 136, there is a gap sufficient for thedownwardly extending arm 136 and hook 138 to pivot out of engagementwith the front tab 108. The security lock 176 includes a contact arm 180which extends in a position to be engaged by a blade 106 as the blade106 is being moved into its extended position. The engagement of thecontact arm 180 by the blade 106 serves to pivot the security lock 176into a position where the locking portion 178 blocks the downwardlyextending arm 136.

With the above described arrangement, the cartridge 104 will bereleasably held in place within the knife body 100, and releasable whenthe blade carrier 116 is in its retracted position and the releasebutton 146 is depressed. When the thumb button 118 moves the bladecarrier 116 into its extended position to expose the knife blade 106,the cartridge 104 is rendered unreleaseable even if the release button142 is depressed. The side release button 146, which will enable removalof the magazine when depressed and the blade carrier 116 is in itsretracted position, also serves to release the blade 106 from the bladecarrier 116 to permit removal of a used blade from the knife body whenthe blade carrier 116 is in its extended position.

Referring to FIGS. 17 a-d there is shown a hobby knife 200 incorporatinga removable blade cartridge 202: The hobby knife 200 includes anelongated body 204 of generally circular cross-section and provided witha blade opening 206 at its front end. A gripping portion 208 is providedadjacent the front end and includes a bottom opening 210 for thereception of the cartridge 202. The cartridge 202 is adapted to holdfive to six blades 212, but other quantities are possible. The blades212 are generally triangular in configuration with a rearward extendingtail portion 214 having a slot 216 therein. The outer surface 217 of thecartridge 202 is arcuate in cross section and provides a generallycontinuous circular surface in cross section with the body 204 wheninserted into the opening 210.

The cartridge 202 is inserted into the opening 210 in the bottom of thegripping portion 208 as shown in FIG. 17 a and is releaseably held inposition by suitable latches (not shown). A thumb button 218 extendsthrough a slot 220 in the body 204 of the knife 200 and is attached to ablade carrier (not shown). The blade carrier is adapted to engage withthe slot 216 in the tail portion 214 of a blade 212. As shown in FIGS.17 b and 17 c, the thumb button 218 is moved forwardly into its forwardposition to extend the blade 212 into its cutting position.

A release button 222 is provided in the side of the body 204. When theblade 212 is in its extended cutting position, depressing the releasebutton 222 as shown in FIG. 17 d will permit the blade 212 to beseparated from the blade carrier and removed from the knife 200. Therelease button 222 will also permit release of the cartridge when thethumb button 218 is moved into its retracted position. The body 204 isprovided with arcuate depressions 224 adjacent the opening 210 toprovide finger access for grasping the cartridge 202 when it is desiredto remove it.

FIGS. 18 a-d show a trimmer 250 of the type adapted to be moved along anarm 252 to trim sheets of paper. The trimmer 250 includes a head member254 mounted for reciprocal movement on the arm 252. The head member 254includes a body 256 having an opening 258 in its top surface 260 for thereception of a blade cartridge 262 holding a plurality of blades 264.The opening 258 is surrounded by a lip 266 that extends over the side ofthe body 256 as shown. One side wall 268 of the body 256 is adapted toride between the two rails 270 and 272 of the arm 252 while the outerside wall 274 is adapted to be positioned on the outside of the arm 252.

The cartridge 262 includes a top surface 276 coextensive with the topsurface 260 of the body 256 including the ribs 278. The top surface 276of the cartridge 262 includes a tongue 280 extending from the side ofthe cartridge 262 and adapted to be received within a slot 282 in thelip 266 on the head member 254. As the tongue 280 extends beyond theside of the body 256, the tongue 280 provides a finger hold for graspingthe cartridge 262 to remove it from the body 256 of the head member 254.The cartridge 262 also includes a downwardly extending ear portion 284on one side having an elongated opening 286 extending therethrough. Theopening 286 provides access to the blades 264 for a blade carrier (notshow) which is connected to a finger button 288 through an elongatedslot 290 in the outer side 274 of the body 256 of the head member 254.The outer side wall 274 and front wall 292 of the body 256 of the headmember 254 have a window 292 provided therein to view the number ofblades 264 remaining in the cartridge 262 while the cartridge 260 isinserted in the body 256.

The blades 264 are circular with a cutting edge extending around theirentire periphery. The blades 264 have a center aperture 294 and anelongated slot 296 as shown. When the cartridge 262 is inserted into thehead member 254, the blades 264 are positioned between the outside ofthe arm 252 and the inner surface of the outer side wall 274 of the body256 of the head member 254. With the cartridge 262 inserted in the headmember 254, the finger button 288 is moved downwardly as shown in FIGS.18 b and c to move. a blade into cutting position. A release button 298is provided in the outer side wall 274 of the body 256 of the headmember 254. When the blade is in its cutting position, depressing therelease button 298 as shown in FIG. 18 d will permit the blade 262 to bereleased from the blade carrier and removed from the head member 254.Depressing the release button 298 when the finger button 288 is in itsretracted position will permit release of the cartridge 262.

While various embodiments have been shown and described, variousmodifications and substitutions may be made thereto. Accordingly, it isunderstood that the present embodiments have been described by way ofillustration and not limitation.

1. A utility knife comprising: a body having a handle portion and afrontal opening for a blade and a receiving cavity opening through saidbody; a cartridge comprising a magazine of blades insertable into saidreceiving cavity; and a carrier manually operable for receiving a bladefrom said received cartridge and positioning said blade for extensionthrough said opening to present a cutting edge.
 2. The utility knife ofclaim 1 further including a button projecting through said body andmanually depressable to release said blade from said carrier to permitwithdrawal forwardly from said opening.
 3. The utility knife of claim 2wherein said button is depressable to allow said cartridge to bewithdrawn from said body.
 4. The utility knife of claim 1 wherein saidcartridge forms a receptacle for receiving a plurality of blades andsaid receptacle defines a detent which interacts to secure saidcartridge to said body.
 5. The utility knife of claim 2 furthercomprising a pivoted lever arm mounted interiorly of said body, said armat one end connected to said button and at a second end engaging saidcartridge to retain said cartridge in said body.
 6. The utility knife ofclaim 1, wherein said cartridge has an exterior surface which mates withsaid body upon reception in said receiving cavity.
 7. The utility knifeof claim 6 further comprising a window opening through said exteriorsurface to allow visual inspection of blades in said cartridge.
 8. Theutility knife of claim 1 wherein said cartridge has a frame and a coverwhich snaps into said frame to capture said blades.
 9. The utility knifeof claim 8 further comprising a biasing member mounted to the interiorof said cover.
 10. The utility knife of claim 8 wherein said frame andcover prevent direct contact with the cutting portion of said blades.11. The utility knife of claim 8 wherein said blades are substantiallycongruent and further include three notches at an upper locationthereof.
 12. The utility knife of claim 8 wherein said cartridge is amolded member.
 13. The utility knife of claim 1 wherein an overmoldsubstantially defines the exterior of said body.
 14. The utility knifeof claim 1 and further comprising a second cartridge receivable in saidreceiving cavity, said second cartridge having a magazine of blades witha configuration different than those of said first cartridge.
 15. Theutility knife of claim 7, wherein said cover further comprises aplurality of protections which form a one-time lock with said frame. 16.The utility knife of claim 15 wherein said blades have a shape typeselected from the group consisting of a trapezoid, a hawk and a hook.17. A utility knife comprising: a body having a handle portion and afrontal opening for a blade and a receiving cavity opening into body; acartridge containing a plurality of blades insertable into saidreceiving cavity, said cartridge having a front and rearward tabs; ablade carrier manually operable for receiving a blade from saidcartridge and moveable into an extended position to position said bladethrough said opening into a cutting position; and front and rearwardcartridge catches adapted to releaseably engage said tabs to secure saidcartridge in said body.
 18. The utility knife of claim 17 furtherincluding a side button mounted in said knife body, said side buttonoperatively connected to said front cartridge catch to release saidfront catch from engagement with said cartridge when depressed.
 19. Theutility knife of claim 18 further including a blocking element for eachof said cartridge catches, said blocking elements being movable intoposition to prevent release of said cartridge catches from said tabswhen said blade carrier is in its extended position.
 20. The utilityknife of claim 19 wherein said rear cartridge catch comprises a slideplate moveable into engagement with said rearward tab, and spring meansurging said sliding plate into engagement with said tab.
 21. The utilityknife of claim 20 wherein said blocking element for said rear cartridgecatch includes a locking block moveable between a first positionblocking movement of said slide plate out of engagement with said taband a second non-blocking position permitting movement of said slideplate out of engagement with said rearward tab.
 22. The utility knife ofclaim 21 wherein said carrier has a portion engageable with said lockingblock to move said locking block into its second position when saidcarrier is retracted.
 23. The utility knife of claim 22 furtherincluding spring means biasing said locking block into its firstposition.
 24. The utility knife of claim 19 wherein said forwardcartridge catch includes a pivotable member having an arm terminating ina hook, said hook adapted to engage said forward tab.
 25. The utilityknife of claim 24 wherein said forward cartridge catch further includesa spring member biasing said hook into engagement with said tab.
 26. Theutility knife of claim 24 wherein said blocking element for said forwardcartridge catch includes a pivotally mounted security lock moveablebetween a first position wherein it blocks said arm of said pivotablemember from being pivoted out of engagement with said tab and a secondposition wherein said arm can be pivoted out of engagement with saidtab.
 27. The utility knife of claim 26 wherein said security lockincludes a contact arm adapted to be engaged by a blade to move saidsecurity lock into its first position as said blade is being moved intoits extended position.
 28. The utility knife of claim 27 wherein saidpivotable member of said forward cartridge catch includes a second armhaving an inclined surface thereon, said side button having an inwardlyextending projection with a surface adapted to mate with said inclinedsurface on said arm whereby axial movement of said push button causessaid pivotable member to rotate to disengage said hook with said tab.29. The utility knife of claim 17 wherein said blade carrier has a thumbbutton operatively connected thereto and extending from said body formoving said carrier between a retracted position wherein it receives ablade from said cartridge to the extended position to position saidblade through said opening to present a cutting edge.
 30. The utilityknife of claim 17 wherein said blades have two notches extending intotheir upper surfaces, and said carrier includes a carrier springoperatively connected thereto, said carrier spring including two bladeengaging elements, one of said blade engaging elements being positionedin a first one of said notches and the second of said blade engagingelements being positioned in said second of said notches.
 31. Theutility knife of claim 30 wherein said one of said blade engagingelements is positioned forward of said second and includes a tabpositioned in the forward notch of a blade for engaging said blade whensaid carrier is moved to its retracted position to retract the blade,and said second blade engaging element comprising a tab extending intothe rearward notch of a blade and serving to engage said blade when saidcarrier is moved to its extended position to move said blade into itscutting position.
 32. The utility knife of claim 31 wherein said one ofsaid first and second blade engaging elements has a portion that ispositioned to be operatively contacted to said push button when saidcarrier is in its extended position to release said blade engagingelements from said blade when said push button is depressed so saidblade can be removed.
 33. A cartridge containing blades for use in aknife, said blades having notches extending downward from their upperedges comprising; a frame for holding said blades, said frame includinga base and a stop plate; a back cover having a spring attached theretofor urging the blades against said stop plate; a break away tabconnected to said frame and extending into a notch in said blades toprevent withdrawal of said blades from said frame; said tab beingcapable of being broken away before insertion of said cartridge into theknife.
 34. The cartridge of claim 33 wherein said blades have twonotches extending downward from their upper edges, said breakaway tabextending into one of said notches and a second tab, connected to saidframe and extending trough the other notches in the blades except forthe blade positioned against said stop plate.
 35. The cartridge of claim33 wherein said blades are generally trapezoidal.
 36. A hobby knifecomprising: an elongated body having a substantially circularcross-section, said body having a gripping portion having a receivingcavity opening into the interior of said body; a cartridge containing aplurality of blades releaseably inserted into said cavity, saidcartridge having an arcuate outside surface providing a continuouscircular surface in cross-section with said body when inserted; and athumb button extending from body to move a blade from the cartridge to acutting position.
 37. The hobby knife of claim 36 further including arelease button projecting through said body and manually depressable topermit a blade to be withdrawn forwardly from said knife.
 38. The hobbyknife of claim 36 wherein said blades are triangular with a tailportion, said tail portion having an elongated slot therein.
 39. Atrimmer comprising: a head member adapted to be reciprocated along anarm, said head member including a body having two side walls and areceiving cavity opening into said body from the top surface thereof, alip surrounding said opening and extending beyond said body; and acartridge containing a plurality of blades releaseably inserted intosaid cavity, said cartridge having a top surface which is continuouswith said top. surface of said head member and including an outwardlyprojecting tongue, said tongue being received in a slot in said lipthereby providing a finger grasping portion removing said cartridge fromsaid head member.
 40. The trimmer of claim 36 wherein said blades arecircular.
 41. The trimmer of claim 37 wherein said arm includes spacerails, one side wall of said body being positioned between said railsand the other outer side wall being positioned outside of said arm, saidblades being positioned within said cartridge such that when saidcartridge is inserted, said blades are positioned between said arm andthe inside surface of said outer side wall.
 42. The trimmer of claim 38further including a finger button extending from a slot in said outerside wall for moving a blade into the cutting position.
 43. The trimmerof claim 39 further including a release button in the side of said ofsaid head member which is manually depressable to release a blade fromthe trimmer.
 44. A knife comprising: a body having a handle portion anda frontal opening for a blade and a receiving cavity opening throughsaid body; a cartridge comprising a magazine of blades insertable intosaid receiving cavity; and a carrier manually operable for receiving ablade from said received cartridge and positioning said blade forextension through said opening to present a cutting edge.
 45. The knifeof claim 44 further including a button projecting through said body andmanually depressable to release said blade from said carrier to permitwithdrawal forwardly from said opening.
 46. The knife of claim 45wherein said button is depressable to allow said cartridge to bewithdrawn from said body.
 47. The knife of claim 44 wherein saidcartridge forms a receptacle for receiving a plurality of blades andsaid receptacle defines a detent which interacts to secure saidcartridge to said body.
 48. A knife comprising: a body having a handleportion and a frontal opening for a blade and a receiving cavity openingthrough said body; a cartridge comprising a magazine of bladesinsertable into said receiving cavity; a carrier manually operable forreceiving a blade from said received cartridge and positioning saidblade for extension through said opening to present a cutting edge, anda button mounted in said body and depressable to allow said cartridge tobe withdrawn from said body.
 49. The knife of claim 48 wherein said abutton projects through said body and is manually depressable to releasesaid blade from said carrier to permit withdrawal forwardly from saidopening.
 50. The knife of claim 49 wherein said cartridge forms areceptacle for receiving a plurality of blades and said receptacledefines a detent which interacts to secure said cartridge to said body.